Narrow Results

Early-stage disease and cancer diagnosis are of particular importance for effective patient identification as well as their treatment. Breath analysis is a promising method for this purpose which can help to detect disease biomarkers. Benzaldehyde and Indole gas molecules as members of volatile organic compounds (VOCs) are composed of a proportion of the exhaled breath and changes in the level of them from breath can be considered for colorectal cancer biomarkers. Due to these incentives, we scrutinized the sensing behavior of Molybdenum disulfide (MoS${}_2)$ toward Benzaldehyde and Indole gas. We inspected the adsorption of the molecules on the pristine and Pd-, Pt-decorated MoS₂ by employing density functional nonequilibrium Green’s function (DFT-NEGF). It was disclosed that the molecules were weakly adsorbed upon the pristine MoS₂. Howbeit, after the decoration of the surface, the adsorption energy and charge transfer of the molecules were improved greatly. On the other hand, the band gap was decreased after metal decoration. For example, adsorption energy of −2.37eV and band gap of 1.32eV were achieved by interaction of Indole with Pd-decorated MoS₂ and it can be desorbed under UV light and at temperature of 698K with recovery time of 12.8s. Ergo, our analysis would help us better understand the adsorption mechanism of Pd- and Pt-decorated MoS₂-based gas sensors. It may open a new route in early disease detection and colorectal cancer monitoring.

The electric-pulse-driven resistance change of metal/oxides/metal structure, which is called resistive switching effect, is a fascinating phenomenon for the development of next generation non-volatile memory. In this work, an outstanding bipolar resistive switching behavior of Ag/MoS₂/fluorine-doped tin oxide (FTO) device is demonstrated. The device can maintain superior reversible stability over 100 cycles with an OFF/ON-state resistance ratio of about 10³ at room temperature.

Au@MoS₂-CdS, as ternary composite structure, was successfully synthesized by a facile process combining hydrothermal and seed-growth methods. The introduction of Au nanoparticles (NPs) into MoS₂ spheres, forming a core–shell structure, demonstrates strong plasmonic absorption enhancement. The incorporation of CdS NPs into the Au@MoS₂ core–shell structure further extends the absorption range of visible light and enhances exciton dissociation. The resultant composite structure exhibits the highest photocatalytic activity in photocatalytic degradation of rhodamine B (RhB) solution, compared with Au NPs, MoS₂ spheres, Au@MoS₂ core–shell and MoS₂-CdS heterostructures. The above phenomena are supported by a series of characterization results such as SEM, TEM, XRD, EDS and UV-Vis, etc. Based on structural and morphological analyses, we propose the synthesis method of ternary composite structure photocatalysts, which is helpful for the synthesis of future multicomponent photocatalytic materials.

n-MoS₂/p-Si heterojunction solar cells were simulated by using Analysis of Microelectronic and Photonic Structures (AMPS-1D) software. In order to fundamentally understand the mechanism of such kind of cells, the effects of electron affinity, band gap and thickness for MoS₂, as well as the donor concentration in Si layer on the devices performance were simulated and discussed in detail. The effects of defect states in Si layer and at n-MoS₂/p-Si interface on the performance of devices were also simulated. It is demonstrated that two-dimensional monolayer MoS₂ with the highest band gap of 1.8 eV is the optimized option for ideal devices which can give out the highest efficiency over 19.0%. Si layer with higher acceptor concentration is more likely to be recommended in achieving higher power conversion efficiency if defect level can be effectively controlled. The defect states in Si layer and at MoS₂/Si interface were identified to influence the performance of the devices significantly.

In molybdenum disulfide (MoS₂), cobalt (Co) doping is an effective way to introduce catalytic active sites on the basal plane. For improving their capability of electrocatalytic hydrogen evolution reaction (HER), it is desirable to produce more active sites and endow them with highly electrocatalytic activity. In this work, we used silicon dioxide (SiO₂) nanospheres as template to prepare porous Co-doped MoS₂ with different Co content. We found that the prepared porous catalyst has improved the catalytic performance. Furthermore, the increase in Co content not only increases the number of active sites, but also can improve the activity for each Co atom. First-principle calculations based on density functional theory (DFT) suggest that this mutually enhanced activity originates from the shift of the density of state (DOS) of the vertical d${}_{z2}$ orbital near the Fermi energy level caused by the interaction among the Co atoms.

Fenton process has been widely applied for environmental restoration. However, acidic and neutral solutions are always needed in order to obtain an excellent catalytic activity. Flower-like MoS₂ was firstly used as a Fenton catalyst with higher activity in alkaline solution than that in acidic and neutral ones. The catalytic mechanism indicated that $•\mathrm{\text{OH}}$ and $•{\mathrm{\text{O}}}_2^{-}$ radicals formation induced the excellent catalytic activity in alkaline solution. Effects of pH, catalyst dosage, H₂O₂ and RhB concentrations on catalytic activity were studied, and the quantitative relations were established. The experimental result demonstrated that the catalyst was stable in alkaline solution. The leaching Mo was smaller than 2mg/L.

Three-dimensional reduced graphene oxide (RGO) matrix decorated with nanoflowers of layered MoS₂ (denoted as 3D MoS₂/RGO) have been synthesized via a facile one-pot stepwise hydrothermal method. Graphene oxide (GO) is used as precursor of RGO and a 3D GO network is formed in the first-step of hydrothermal treatment. At the second stage of hydrothermal treatment, nanoflowers of layered MoS₂ form and anchor on the surface of previously formed 3D RGO network. In this preparation, thiourea not only induces the formation of the 3D architecture at a relatively low temperature, but also works as sulfur precursor of MoS₂. The synthesized composites have been investigated with XRD, SEM, TEM, Raman spectra, TGA, N₂ sorption technique and electrochemical measurements. In comparison with normal MoS₂/RGO composites, the 3D MoS₂/RGO composite shows improved electrochemical performance as anode material for lithium-ion batteries. A high reversible capacity of 930mAh$\cdot$g${}^{-1}$ after 130 cycles under a current density of 200mA$\cdot$g${}^{-1}$ as well as good rate capability and superior cyclic stability have been observed. The superior electrochemical performance of the 3D MoS₂/RGO composite as anode active material for lithium-ion battery is ascribed to its robust 3D structures, enhanced surface area and the synergistic effect between graphene matrix and the MoS₂ nanoflowers subunit.

Based on U-g-C₃N₄ (U-gCN) and T-g-C₃N₄ (T-gCN) prepared with urea and thiourea as raw materials, respectively, a visible-light-driven MoS₂-modified U-gCN/T-gCN/MoS₂ (UTM) ternary heterojunction photocatalyst was successfully prepared using a sonication and bathing method. The photocatalytic activity of as-prepared photocatalyst was evaluated through the degradation of tetracycline hydrochloride (TC) and Rhodamine B (RhB) under the visible light irradiation. The UTM ternary heterojunction showed remarkably enhanced photocatalytic activity. For the degradation of TC and RhB, the degradation rates of 93.9% and 99.9% have been achieved after being irradiated under visible light for 2h and 1h, respectively. The enhanced photocatalytic performance can be ascribed to the role of loaded MoS₂ cocatalyst and the well-formed interfaces between U-gCN and T-gCN, which not only enhance the light absorption, but also accelerate the separation and transfer of photogenerated electron–hole pairs. Furthermore, UTM ternary heterojunction has excellent recyclability and chemical stability. The photodegradation rates of 89.9% and 96.78% of TC and RhB have been obtained, respectively, after being reused for five times. Sacrificial agent tests demonstrate that $•$${\mathrm{\text{O}}}_2^{-}$ is the major reactive species in the photocatalytic reaction system.

A surfactant system L64 and alcohol mixture was employed to exfoliate MoS₂. To reduce the impact of surfactant on the quality of the nanosheet, the concentration of L64 was decreased to an extremely low value 0.0325 mM. Utilize common ultrasonic bath, the production yield of the nanosheet was increased to about 5% per hour, and statistical results from AFM showed that 40% of the nanosheet were less than 4 nm thick. Rheology characterization showed that surfactant alcohol mixtures were shear thinning fluid, yet the viscosity of L64 system varies directly with the shear rate in the high-speed shear region (higher than 400 s⁻¹), and further affect the shear strength, therefore viscosity at high-speed shear can be considered as an indicator of the effectiveness for the exfoliation system. Exfoliated MoS₂ was evaluated by hydrogen evolution reaction, and compared to the bulk MoS₂, the 4 wt% Pt/FL-MoS₂ improved the overpotential from 366 mV to 273 mV at 10 mA$•$cm${}^{-2}$. This study presented a facile and effective route to fabricate 2D MoS₂ with much less residue, and bring more opportunities to exploit clean and nontoxic system to exfoliate 2D materials.

MoS₂ self-lubricating films were prepared on long-range ordered porous anodic alumina (PAA) by an electrophoretic deposition (EPD) method. The PAA was prepared by two-step anodization of aluminum plates. Oxalic-acid-based electrolytes were used in the first step and phosphoric-acid-based electrolytes were used in the second step. This process offers a new approach to preparing PAA with wide adjustable boundary distances (43.5–21 nm) by increasing the voltage from 80 V to 100 V. The boundary distances were decreased from 78 nm to 42.2 nm by increasing the solution concentration, which increased the interpore distance. The coefficient of friction and hard-wearing of the MoS₂ lubrication film on the PAA were studied by a ball-on-disk friction and wear tester. The results showed that the nanotubes stored MoS₂ particles, which provided continuous lubrication.

A broadband MoS₂-based absorber composed of Ag rod/MoS₂/dielectric/Ag is proposed in the visible band. The relative bandwidth is 65% for the absorption above 80%. The absorber also has the properties of polarization-independence and wide-angle absorption. Impedance matching theory is used to analyze the physical mechanism of the broadband absorption. By investigating the absorption property of each part of the absorber, it is found that the absorption is enhanced by introducing the two-dimensional material MoS₂. The broadband absorber can be changed to be multiband absorber by changing the thickness of dielectric substrate. This structure provides a new perspective to enhance absorption in the visible band and has promising applications in solar cells.

In this study, the surface acoustic wave device combined with an oscillator circuit was used as the excitation platform to explore the photoluminescence responses of the two-dimensional atomic layers of MoS₂. The MoS₂ layers were prepared using the mechanical exfoliation method, and then transferred onto the SAW delay line area of the platform. Under the varied servo driving voltages of the excitation platform, various power intensities of the oscillator were obtained. It represented that the various energy levels of acoustic waves were propagated underneath the MoS₂ layers. From the observation by multiphoton excitation microscopy, the excited fluorescent intensities of the MoS₂ species were detected at various levels. Studies have proved that as the driving voltage of the oscillator increases, the interaction between the MoS₂ species and the acoustic wave is also enhanced.

To improve the high charge carrier recombination rate and low visible light absorption of {001} facets exposed TiO₂ [TiO₂(001)] nanosheets, few-layered MoS₂ nanoparticles were loaded on the surfaces of TiO₂(001) nanosheets by a simple photodeposition method. The photocatalytic activities towards Rhodamine B (RhB) were investigated. The results showed that the MoS₂–TiO₂(001) nanocomposites exhibited much enhanced photocatalytic activities compared with the pure TiO₂(001) nanosheets. At an optimal Mo/Ti molar ratio of 25%, the MoS₂–TiO₂(001) nanocomposites displayed the highest photocatalytic activity, which took only 30min to degrade 50mL of RhB (50mg/L). The active species in the degradation reaction were determined to be h${}^{+}$ and ${}^{•}$OH according to the free radical trapping experiments. The reduced charge carrier recombination rate, enhanced visible light utilization and increased surface areas contributed to the enhanced photocatalytic performances of the 25% MoS₂–TiO₂(001) nanocomposites.

Constructing van der Waals (vdW) heterostructures with various-layered two-dimensional (2D) materials is attractive to design various materials and devices. For controllable fabrication of vdW heterostructures, it is very important to make the growth process clear. In this work, SnS₂/MoS₂ vertical heterostructures were synthesized by the one-step chemical vapor deposition (CVD) method. The bottom MoS₂ triangle layers can be partially or completely covered by SnS₂ layers. The interlayer charge separation was also observed in the heterostructures by photoluminescence (PL) spectroscopy. The growth mechanism of SnS₂/MoS₂ vertical heterostructures was also discussed for the first time. MoS₂ triangle layers form on the substrates at first and then grow a top layer of SnS₂. This study will provide an important and practical method, as a guidance to prepare high-quality vertical heterostructures.

We study Hall and Nernst transports in monolayer MoS₂ based on Green’s function formalism. We have derived analytical results for spin and valley Hall conductivities in the zero temperature and spin and valley Nernst conductivities in the low temperature. We found that tuning of the band gap and spin-orbit splitting can drive system transition from spin Hall insulator (SHI) to valley Hall insulator (VHI). When the system is subjected to a temperature gradient, the spin and valley Nernst conductivities are dependent on Berry curvature.

The ability of MoS₂ nanomaterials as adsorbent and photocatalytic materials of methylene blue (MB) dye after $\gamma$-ray irradiation is investigated. The MoS₂ nanomaterials are prepared by a simple hydrothermal route, and then irradiated with Co-60 gamma radioisotope at different doses of 1, 10, 100, 1000 kGy. All the samples are characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Diffusivity Reflectance Spectroscopy (DRS) and Brunauer–Emmet–Teller (BET). The XRD analysis shows no change in crystal structure of MoS₂ nanomaterials after irradiation. The DRS analysis indicates the optical bandgap increases from 1.73 to 1.82, 1.86, 1.94 and 2.00 eV, respectively. The performance of the dye-absorbing solutions and the photocatalytic dye solutions before and after irradiation is compared. After $\gamma$-ray irradiation, the adsorption capacity of the MoS₂ nanomaterials degrades, which can be attributed to the decreased specific surface area, from 77.060 to 48.812, 35.855, 38.789 and 27.137 m²/g, respectively. The photocatalytic degradation ability for the MB solution also decreases due to the increase of optical bandgap of the samples after $\gamma$-ray irradiation.

In this paper, we study Hall effects of the monolayer MoS₂ with Rashba and Ising spin-orbit coupling (SOC) under the application of a circularly polarized light. The Chern number and spin textures at high frequency regime are studied based on the Floquet theory. We found that the SOCs induced valley Hall effect. The sign of Chern numbers at high frequency regime can be reversed by engineering interplay between Ising SOC and light intensity. The system undergoes a topological phase transition from valley Hall state to anomalous Hall state. By analyzing the spin texture, we study the origin of the Hall effects.

The effect of biaxial strain on O-doped monolayers MoS₂ has been systematically studied by the first-principles calculations. It is shown that the strain decreases the structural stability of O-doped monolayer MoS₂. Between 0% and 12% tensile strains, the bandgap steadily narrows. At different compression strains, the bandgap increases and then decreases. The optical properties analysis shows that the strain causes the peaks of both the real and imaginary parts of the dielectric function to appear in the low energy region. And it affects the absorption and reflection peaks of the doping system so that it has a strong absorption of photons in the ultraviolet region. The doping system shows resonance in the range of 0–10eV. The results of this study verify that strain can properly regulate the electronic and optical properties of O-doped monolayer MoS₂, and provide a theoretical reference for the implementation of MoS₂ in optoelectronic devices.

In the quest of extending isostructural hybridization approach to organic–inorganic nanocomposite-based photocatalytic systems, a unique strategy of replacing the traditional inorganic semiconductors with naturally produced mycosporine-like amino acids (MAA) is proposed. The main motivation of incorporating MAA in symbiotically configured nanocomposites is with regard to MAA green, nontoxic nature, UV absorption and photostability. Our facile one-pot solvothermal method is to facilitate the amalgamation of MAA and molybdenum disulfide-graphene (MG) composite at the molecular/nanoscale level to endow better photocatalytic functionality. It is observed that the rate of photocatalytic dye degradation of Rhodamine 6G (R6G) becomes consistently enhanced with an incremental increase in the concentration of MAA in MG. The combination of MG-MAA leads up to 81.2% quenching of the PL emission, as compared with MG. Noticeable decrease in PL lifetime from 280 ps (MG) to 77ps (MG-MAA) explicitly implies fast charge extraction and transport of the charge carriers.

Nanoparticles (NPs) with high uniformity have been extensively investigated for their excellent chemical stability. Near-monodisperse globular MoS₂ NPs were prepared with sulphur powders (SPs) as a sulphur source by a one-pot polyol-mediated process without surfactants, transfer agents and toxic agents at 170–190${}^{\circ }$C. The as-processed SPs greatly affected the formation of the MoS₂ NPs after low-activity sulphur (S₈)_n was reassembled from common SPs (S${}_8)$. The average size of MoS₂ NPs can be reduced remarkably from 100–200nm to 50nm by introducing low amounts of MnCl₂. A preliminary four-step growth mechanism based on the aggregation-coalescence model was also proposed. This green and simple method may be an alternative to the common hot-injection and heating-up methods for the preparation of monodisperse NPs, particularly transition metal dichalogenides.